- Males and females at each nest were captured within 24 hours of each other approximately 7 days after the hatching of their chicks.
- Mass was measured to the nearest 0.5 g using a spring scale.
- Size-specific mass (mass/wing length3) presumably reflects fat reserves. Wing length was measured to the nearest 0.5 mm.
- Bilateral asymmetry measures the degree to which individuals are developmentally buffered against environmental stressors. Birds with perfect bilateral symmetry are presumed to be high quality individuals. Our measure of symmetry was the difference in length (0.01 mm) of the left and right outer tail feathers.
- Hematocrit, the ratio of red blood cells to total blood volume, is often used as an index of physiological health. Measured by centrifuging small blood samples taken at capture.